Recently, there is an accelerating demand to mount touch panels as the screen on mobile phones and other displays. While the touch panel has a screen kept bare, there are many chances of the finger or cheek coming in direct contact with the screen. Undesirably the touch panel is readily fouled with stains like sebum. There is an increasing need for technology to attain fingerprint proofness or easy stain removal on a surface of a display for better appearance or visibility. The prior art water/oil repellent agents can form films having the advantages of high water/oil repellency and easy stain wipe-off. However, since these agents tend to agglomerate together, they are difficult to form flat or smooth films, and haze often becomes a problem. It is thus desired to develop a treating agent and method capable of forming a high-performance film in a consistent manner while suppressing any haze increase.
Generally, fluoropolyether-containing compounds exhibit, by virtue of their extremely low surface free energy, water/oil repellency, chemical resistance, lubricity, parting, antifouling and other properties. Taking advantage of these properties, they find use in a variety of industrial fields as water/oil repellent antifouling agents for paper and textiles, lubricants for magnetic recording media, oil-repellent agents for precision instruments, parting agents, cosmetic ingredients, protective films and the like. Inversely, the same properties indicate non-tackiness or non-adhesion to other substrates. Even if they can be coated to the substrate surface, it is difficult for the coating to tightly adhere thereto.
On the other hand, silane coupling agents are well known for their ability to bond surfaces of glass or fabric substrates to organic compounds. They are widely used as surface coating agents for numerous substrates. The silane coupling agent contains an organic functional group and a reactive silyl group (typically alkoxysilyl) in the molecule. In the presence of airborne moisture or the like, the alkoxysilyl groups undergo self-condensation reaction to form a coating. As the alkoxysilyl groups form chemical and physical bonds with the surface of glass or metal, the coating becomes a tough coating having durability.
Patent Document 1 discloses a linear fluoropolyether group-containing silane represented by the formula shown below.
Herein Rf is a divalent linear fluoropolyether group, R is C1-C4 alkyl or phenyl, X is a hydrolyzable group, n is an integer of 0 to 2, m is an integer of 1 to 5, and a is 2 or 3. When treated with this fluoropolyether group-containing silane, glass, antireflective coatings and other substrates are improved in lubricity, parting property and wear resistance. However, since a non-fluorinated group is included in the terminal groups, there is a chance that non-fluorinated groups agglomerate together during or after the coating step, detracting from transparency and other optical properties of the substrate.